In order to join or connect, or to provide a connecting peg means, in medullated bones, in which the bone marrow spike must be driven into a duct in the bone, outside of the joint area, at an acute angle relative to the longitudinal axis of the bone, as is the case, for example, when joining or connecting bones of the lower leg, use is made, in modern bone surgery, primarily of standardized, slotted, tubular bone marrow spikes, which are curved and provided with a surface profile. One end section of such types of spikes is tapered and serves as guide when driving in the spike. The other end section of such types of spikes has a face perpendicular to the axis of the spike and serves for the application of the tool for driving the spike into the bone. The outer surface area of the spike has a longitudinal profile, which gradually disappears toward the leading end. On the leading end, the spikes generally have a ring-shaped section.
In intramedullary pegging or connecting, it is important for the healing success that the bone marrow spike be anchored in the bone in such a way that it is secure against twisting. Therefore, one important requirement is that the inserted bone marrow spike can find reliable all-around support against the corticalis at the point of insertion, i.e., against the surface of the duct in which the spike is inserted in the bone, with the spike finding sufficient support both on the portion of the surface area which, viewed from the inserted spike, is pointing against the surface of the bone, and against the portion disposed adjacent the inner bone marrow duct. If the spike is additionally provided with a suitable longitudinal surface profile, torsional stability is also reliably assured without totally excluding the possibility of a sliding motion between the spike and the bone and which motion in a longitudinal direction is desirable for the healing success.
Known curved intramedullary spikes with a leading face extending perpendicularly to the axis of the spike have a number of basic drawbacks if inserted into a duct extending in an inclined direction with respect to the surface of the bone. If they are driven only to a depth sufficient to still assure reliable support of the leading end against the corticalis of the total overall spike-receiving duct in the bone, the end of the spike necessarily projects beyond the surface of the bone and comes into contact with the connective tissue covering the bone. This results in pain, tissue infection and similar complications for the patient. On the other hand, if the spike is driven into the bone to a depth sufficient to prevent it from projecting from the surface of the bone, its contact area with the surface of the spike-receiving duct facing the medullary canal is insufficient to reliably assure torsional stability as a result of its surface profile, if any such stability is still available at all, within the end zone of the spike. In such unfavorable cases, the spike may even break through the corticalis into the medullary canal. Consequently, when the above conditions exist, the spike has no torsional stability at all and fails to provide the fixation of the fractured bone parts which is required for healing. Furthermore, a medullary spike, once completely inserted in the medullary canal, is difficult to extract and causes a severe bone defect.
Intramedullary spikes which are provided on their leading ends with an internal thread into which a striking sleeve is screwed are known and they can be driven into the spike-receiving duct in the bone without direct hammering on a face area. However, such spikes generally have an area perpendicular to the axis of the spike on the face side and are, furthermore, normally not provided with a profilated or shaped or curved surface area on the inserted end. Consequently, the drawbacks outlined above apply also to spikes such as these when they are inserted in a spike-receiving duct extending into the bone at an inclination.
In addition, spikes are known which have their leading ends shaped approximately in the form of a round head. The above-mentioned drawbacks also apply to spikes of this type, though to a lesser extent.
An intramedullary two-part spike with rotational stability is disclosed in British Pat. No. 817,525. This spike, once fixed in the bone, has a leading end with a divided face area due to the different depths to which the individual parts of the spike are driven into the bone. Since the two parts of the spike are inserted one after the other, the driving tool cooperates not with said divided surface, but in each case only with the nondivided surface of each individual part of the spike. The projection of larger portions of the spike from the surface of the bone is practically unavoidable with this design of intramedullary spike.
It is the object of the present invention to eliminate the above shortcomings of intramedullary lower leg spikes which are to be driven into a spike-receiving duct in the bone in a direction radically deviating from the vertical line. It is a further object of the invention to provide intramedullary lower leg spikes which rest within the zone of insertion on the total bone tissue with torsional stability all-around, without projecting from the surface of the bone and without causing the aforementioned complications for the patient.